Ovariectomy does not attenuate aggression by primiparous lactating female rats.

Nulliparous female hooded rats were allowed to cohabit with a sexually active male in a large living cage. Aggression toward an unfamiliar female was assessed during the second and third week of pregnancy. Within 12 to 24 h following parturition females were ovariectomized (n = 7) or sham-ovariectomized (n = 6) in a manner that balanced previous aggression scores. Aggression was assessed at 48 h following ovariectomy and at three weekly intervals thereafter. Ovariectomized and sham-ovariectomized females did not differ in the number of attacks, number of bites, duration of on-top, or frequency of piloerection on any test day following parturition. These results indicate that circulating levels of ovarian steroids do not influence the level of aggression by a primiparous lactating female toward an unfamiliar female conspecific.